Photochemical reactions of N-(phenylalkyl, 2-pyridyl, or 2-pyridylmethyl)-o-sulfobenzoic imides

Photochemical reactions of N-(phenylalkyl, 2-pyridyl, or 2-pyridylmethyl)-o -sulfobenzoic imides 2-5 were examined in ethanol and benzene solutions. Ir radiation in ethanol afforded benzamides 7, 9, 11, 14, and in benzene solut ion 2-phenylbenzamides 8, 10, 12, 15 were obtained. Irradiation of N- (2-py ridyl)-o-suliobenzoic imide(5) generated benzo[c][1,8]naphthyridin-6 (5H) - one(13) as an additional product. This photocyclization was clarified to pr oceed via the S-1 state by the triplet quenching experiment. Those photoche mical reactions were proposed to occur via a biradical formed by extrusion of SO2. On ESR measurement of N-propyl-o-sulfobenzoic imide(1) irradiated i n the methanol matrix at 15 K, the signals of a monoradical of g=2.0048 and a methyl radical were observed, but the existence of the biradical was not confirmed.